Process for producing pigment nanoparticle

ABSTRACT

The process for producing highly concentrated nanometer-size fine particles of an organic pigment, which comprises dissolving the organic pigment in an amide solvent, especially an organic solvent comprising at least 50 vol % 1-methyl-2-pyrrodinone, and pouring the resultant organic pigment solution with stirring into a poor solvent which is not compatible with the organic pigment. The pigment may be a quinacridone pigment, phthalocyanine pigment etc. Any atmospheric pressure to a sub-critical and/or supercritical state can be employed as the production conditions.

FIELD OF THE INVENTION

The present invention relates to a method for preparation of organicpigment fine particles with nanometer size, especially organic pigmentfine crystal particles with nanometer size, comprising, preparing highconcentrated solution of organic pigment by using organic solutioncomposed of amide solvent, then pouring said solution into poor solventflow to above mentioned organic pigment under stirring, and preparinghigh concentrated dispersion of nanometer size fine particles of saidorganic pigment.

The term of “under stirring” means the stirring or mixing speed of2000±1500 rpm in the case of use of a rotary stirrer, or means thestirring condition such as turbulent condition in the case ofsub-critical or supercritical state.

BACKGROUND OF THE INVENTION

Since organic pigments have abundant hue, and good properties forcoloring performance and transparency, are extensively applied as acoloring agent in various fields such as printing ink, ink for ink-jet,color toner for electronic photograph, color filter, reflection typedisplay, cosmetics, and plastics. Further, several kinds of organicpigments are being investigated as functional materials in technicalfields, being different from the use as the coloring agent, e.g.,photoelectronic property or EL property, and are used as a constitutivematerial by utilizing said properties. In the case to use pigment inabove mentioned various applications, particle size of pigment, shape ofpigment and crystal form of pigment are the important properties, whichaffects to dispersability, coloring ability, weather resistance, lightresistance and heat resistance at processing (Document 1: Dyes andpigments 21(1993) 273–297). For example, in a liquid type productcontaining an organic pigment for printing ink or ink for ink-jet, it isvery important factor to control particle size and crystal form ofpigment and to arrange the particle size distribution, for theimprovement of thixotopic ability, coloring ability and dispersestability in the preservation of pigment. Further, the control ofparticle size of pigment, crystal form, and uniformity of particle sizeof pigment are important factors which affect to electrostatic stabilityin the use of toner for electronic photograph pigment, coloring abilityand dispersing stability in cosmetics, and light resistance and weatherresistance. Furthermore, in the development of above mentionedfunctional materials, it is important to find particle size, crystal anduniformity of particles size, and characteristics as the functionalmaterials such as photoelectronic property, EL property, and to optimizethe related photoelectric conductive property as well as the developmentof pigment derivatives with suitable function.

It is ideal that a product having properties requested for the organicpigment can be obtained by improving a synthesis method of organicpigment, however, at the present time, the method for preparation oforganic pigment is not achieved to the technical level to satisfy saidideal situation. In particular, since quinacridone pigments andphthalocyanine pigments are superior in stability and safety as acoloring agent, these pigments are expected to be used in the field ofphotoelectronic property and EL property, and a new method forpreparation of organic pigment particles is investigated. However, in anorganic pigment obtained by new method, it is necessary to purify thesynthesized crude pigment to control the particle size so as to adjustthe desired condition, and to adjust the crystal form to cause therequired characteristics as the coloring agent and the functionalmaterials through the solvent post-treatment process.

Since the purpose of these treatment processes for the crude pigment iscoincident to the requirement as the pigment, these treatments arecalled as pigment formation treatments.

In the meanwhile, since these pigments are generally insoluble in normalsolvent, the pigment formation treatment contains various processes suchas grinding, crystallization from sulfuric acid solution, and washing ofcrystallized particles, therefore, are not sufficient from the viewpoint of energy consumption and environmental suitability (orversatility). And from the view point of characteristics of product,these pigments are not so the ideal, that is to say, the particle sizeis enough small monodispersed.

The inventors of the present invention have continued a development andan investigation of the technique to prepare nanometer size particles oforganic compound. And in said development, the inventors of the presentinvention have established a technique called as re-precipitation method(Document 2: JP6-79168 publication). Namely, solution of organiccompound is prepared using relatively easy-handling organic solvent,said prepared solution is poured into solvent which is poor solvent forsaid organic compound and is compatible with the organic solvent usedfor the preparation of the solution, by vigorous stirring, and thennanometer size particles of the organic compound by reprecipitation arefabricated.

In [0008] of the document 2, there is a description that [On the otherhand, acid pasting method characterized by dissolving organic compoundwhich is insoluble in normal solvent such as phthalocyanine pigment insulfuric acid, accompanied with reaction to some extent, then dispersinginto water and obtaining fine particles by mixing is disclosed, forexample, in “The Phthlocyanines II” p. 35–37, F. H. Moser et al (1983,issued by CRC Press). This is a specific method to obtain fine particlesof pigment, and since a strong acid is used, kinds of applied materialto be used are limited, and the purity is in general lowered.].

Further, the inventors of the present invention also proposed the methodfor preparation of sub micron fine crystals of quinacridone pigment fromcrude quinacridone pigment particles, using reprecipitation method fromsupercritical or sub-critical solution [Document 3, WO 02/092700 A1,21.11.02 International Publication, JP Laid Open Publication2002-580681, laid open on May 15, 2002 (JPA 2001-144706)].

In this document, there is a description that quinacridone pigments withnanometer size can be obtained, however, it is not complete as theindustrial production method. As a competitor to supply said pigments,suppliers of India and China are starting to join in the market,therefore, the development of a technique aiming mass production of highquality product is becoming the necessitated condition to overcome thecompetition with the competitors.

As a technique which can replace with the technique using sulfuric acid,there is a Paper from Allide Chemical Co., Ltd., reporting that crudequinacridone is heated in 8 times volume of polyphosphoric acid (PAA) at85° C. to 100° C. for 4 to 18 hours, poured into methanol of 20 timesvolume, boiled for 1 hour, after washing by water, bright red or purplepigment is obtained. Further, the Paper describes that when crude β typequinacridone is dissolved in PAA and regenerated by lower aliphaticalcohol, β type changes to γ type, however, if treated by modifiedalcohol, quinacridone can maintain β type. Furthermore, there is a Paperreporting that the important factors to affect the product aretemperature to cause regeneration, purity of alcohol and adding speed ofalcohol. [Document 4, Yosio Nagai, Hisao Nishi “Dye and Drug” Vol 13, p81–107 (88–89), (1968)].

Still further, in 9–15 page of “Journal of the Imaging Society of Japan”Vol. 37, No. 4, there is a description the preparation of α typeoxotitaniumphthalocyanine pigment (hereinafter, abbreviated term: Pcpigment) comprising, forming a charge generating layer in aphoto-semiconductor by dispersing α type oxotitaniumphthalocyaninepigment into a binder resin, the particle size of the Pc pigment used is0.1 μm or less, and by refluxing in acetonitrile for 20 hours or inchloroform for 10 hours to obtain Pc pigment with said particle size anddesired crystal form (page 10).

However, above mentioned pigment formation treatments, which do not usesulfuric acid, are not sufficient from the view point of simplicity andproductivity. Therefore, it is very important to develop a pigmentformation treatment technique, which dissolve problems referring toenvironment and energy, and to obtain organic pigment having desiredpigment particle size and crystal form.

The subject of the present invention is to provide a pigment formationtreatment technique, which dissolves the problems of conventionaltechnique, and is available from the view point of industrialproduction. The inventors of the present invention continued an eagerinvestigation to dissolve said problems using various solvents, andfound that the amide solvents heated at high temperature can dissolveorganic pigments, which does not indicate solubility in the organicsolvents, especially quinacridone pigment or phthalocyanine pigment athigh concentration. And, found that high concentrated pigment dispersioncan be prepared by pouring the obtained solution into poor solvent tothe pigment, especially into sufficiently cooled poor solvent, byvigorous stirring. Thus, said subject can be dissolved.

Further, the inventors of the present invention have found accidentallythat among amide solvents, 1-methyl-2-pyrrolidinone has a specificsolvent property that indicates into layers of polycyclic aromaticcompound such as coal, and dissolve it, and can dissolve organic pigmentat high concentration by breaking strong intermolecular interactioncaused between planar electron conjugated molecules. Said accidentaldiscovery and re-precipitation method which investigated eagerly by theinventors of the present invention are combined, and said subject can bedissolved.

DISCLOSURE OF THE INVENTION

The present invention is (1) the method for preparation of highconcentrated nanometer size fine particles of organic pigmentcomprising, after dissolving organic pigment in organic solvent composedof amide solvent, pouring the obtained pigment solvent into solution,which is compatible with said solvent and is poor solvent to thepigment, by vigorous stirring. Desirably, (2) the present invention isthe method for preparation of high concentrated nanometer size fineparticles of organic pigment of (1), wherein the organic pigment is azopigment, phthalocyanine pigment, quinacridone pigment isoindolinonepigment, cyanine pigment, merocyanine pigment, fullerene pigment,polycyclic aromatic compound or polydiacetylene pigment, furthermoredesirably, (3) the present invention is the method for preparation ofhigh concentrated nanometer size fine particles of organic pigment of(2), wherein the organic pigment is phthalocyanine pigment orquinacridone pigment.

And desirably, (4) the present invention is the method for preparationof high concentrated nanometer size fine particles of organic pigment of(1) to (3), wherein the amide solvent is at least the one selected fromthe group consisting of 1-methyl-2-pyrrolidinoe,1,3-dimetyl-2-imidazolidinone, 2-pyrrolidinone, ε-caprolactum,formamide, N-methylformamide, N,N-dimethylformamide, acetoamide,N-methylacetoamide, N, N-dimethylacetoamide, N-methylpropaneamide andhexamethylphospholictriamide, further desirably, (5) the presentinvention is the method for preparation of high concentrated nanometersize fine particles of organic pigment of (1) to (4), wherein employedpoor solvent is water, alcohol solvents, ketone solvents, ethersolvents, aromatic solvents, carbon disulfide, aliphatic solvents,nitrile solvents, sulfoxide solvents, halide solvents, ester solvents,ionic solution or mixed solution consisting of these two or moresolvents, furthermore desirably, (6) the present invention is the methodfor preparation of the organic pigment of nanometer size fine particlesof organic pigment of (2) to (3), using solvent consisting of at leastthe one selected from the group consisting of 1-methyl-2-pyrrolidinone,2-pyrrolidinone, 1,3-dimetyl-2-imidazolidinone, or a mixed amide organicsolvent containing said solvents more than 50 volume % as a solvent forthe organic pigment, and using water and/or alcoholic solvent as a poorsolvent.

Moreover, desirably, (7) the present invention is the method forpreparation of nanometer size fine particles of (1)–(6) comprising,carrying out the preparation of solution by dissolving an organicpigment under the conditions of heating at around maximum boiling pointunder atmospheric pressure to supercritical state, then pouring theprepared high concentrated organic pigment solution of 0.5 mmol/L–100mmol/L into a poor solvent of liquid state at the lowest temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the Scanning Electron Microscope (SEM) observation ofquinacridone crystal of Example 1 which is obtained by using water as apoor solvent.

FIG. 2 shows the distribution of average particle size of thequinacridone crystal of Example 1 by observing the size of obtainedquinacridone crystal by naked-eye observation of SEM image of Example 1.

FIG. 3 shows the powder X ray diffraction pattern of nano quinacridonecrystal of Example 1. The pattern has 3 peaks at 6.099, 13.816 and26.153 of 2 θ, and said crystal can be confirmed as γ type.

FIG. 4 shows the powder X ray diffraction pattern of nano quinacridonecrystal of Example 1 which is obtained by using methanol as a poorsolvent. Since the pattern has a peak at 26.870 of 2 θ, said crystal canbe considered as α type.

FIG. 5 shows the absorption spectrum of water dispersion liquid of nanoquinacridone crystal prepared by changing the solution concentrationpoured into water, which is poor solvent, to 1 mM (a), 3 mM (b), 5 mM(c) and 10 mM (d).

FIG. 6 shows the absorption spectrum of water dispersion liquid of nanoquinacridone crystal obtained in Example 1 (a) and (b). (a) has twopeaks at 520 and 550 nm, therefore can be confirmed as γ type.Absorption peak position of (b) is beyond 600 nm, therefore can beconfirmed as α type.

FIG. 7 shows the SEM observation of nano titanyl phthalocyanine crystalobtained in Example 3.

FIG. 8 shows the distribution of average particle size of the nanotitanyl phthalocyanine crystal of Example 7 prepared by measuring thesize of obtained nano titanyl phthalocyanine crystal from naked-eyeobservation of SEM image of Example 7.

FIG. 9 shows the powder X ray diffraction pattern of nano titanylphthalocyanine crystal of Example 3. Since the pattern has one strongpeak at 26.49 of 2 θ, said crystal can be said a new crystal form whichwas not found so far.

FIG. 10 shows the absorption spectrum of mixed poor solvent dispersionof water and t-butanol of nano titanyl phthalocyanine crystal.

PREFERRED EMBODIMENT OF THE INVENTION

The present invention will be described in more detail.

A. A pigment which can apply the method for preparation of fine particleof pigment of the present invention is a pigment comprising, havingsufficient solubility with an organic solvent consisting of amidesolution, being compatibility with said amide solution such as water,alcohol solvents, ketone solvents, ether solvents, aromatic solvents,carbon disulfide, aliphatic solvents, nitrile solvents, sulfoxidesolvents, halide solvents, ester solvents or ionic solution and beingpossible to exist a combination of solvents to be poor solvent for thepigment (definition: solubility is 1 μmol/L or less). Concerningquinacridone pigments, phthalocyanine, in particular, metalphthalocyanine pigments or diazo pigments which become possible to applythe method for preparation of fine particle of pigment by using mixedpoor solvents such as water and alcohol solvents e.g. lower alcohol,which carbon number is 4 or less, or acetone, it is very advantageous,because nanometer size crystal particles of these pigments are verydifficult to obtain by conventional methods.

As the desirable amide solvent, 1-methyl-2-pyrrolidinone,2-pyrrolidinone or 1,3-dimetyl-2-imidazolidinone can be mentioned.

B. In the present invention, it is possible to add cationic, anionic ornonionic surfactants for the purpose to adjust the crystal form of fineparticles and to control the formation of secondary particles. Areactive surfactants are also advantageous to the preparation of fineparticles.

C. As the preparation condition of organic pigment solution, temperatureof boiling point of the solvent or less in atmospheric pressure tosub-critical and/or super critical conditions can be adopted. Refluxingcondition can be also adopted.

Highly concentrated solution of organic pigment is desirable from theview point to prepare high density pigment dispersion, however,concerning facilitation for solution preparation and productivity,desirable range of concentration is 0.5 mmol/L to 100 mmol/L. From theview point of equipment, the temperature condition of boiling point ofthe solvent in atmospheric pressure is profitable.

D. Condition of poor solvent is the injection speed which adjust thedepositing condition of pigment, and is possibly lower temperaturecondition than said organic pigment solution, and can select the rangefrom atmospheric pressure to sub-critical, super critical condition.

Incidentally, the injection speed of the solution poured (10 μL–400 mL)is 10 μL/sec to 10 mL/sec for 1 mL to 50 L of poor solvent. In the caseto stir the poor solvent, the stirring is carried out under turbulentcondition, aiming to depress the formation of secondary particles,specifically a rotary stirrer is used at 2000±1500 rpm condition.

EXAMPLES

The present invention will be described more in detail by Examples.However, these examples intend to indicate the usefulness of the presentinvention, and not to limit the scope of the present invention.

Example 1

1, 3, 5 and 10 mM of non substituted and chained quinacridone pigmentare respectively dissolved in 200 μL of 1-methyl-2-pyrrolidinone [commonname: N-methylpyrrolidinone (NMP)] at room temperature and obtaineduniform solution. Said prepared solutions are poured into 10 mL of waterwhich is vigorously stirred by 1500 rpm. SEM photographs of the obtainedfine particles of quinacridone pigment is took, and the image isvisually observed and the size of formed particles of quinacridonepigment is measured and distribution of average particle size isdetermined. SEM image is shown in FIG. 1, distribution of particles sizeis shown in FIG. 2. Average crystal size of the quinacridone pigmentcalculated from said measurement is 20 nm.

Powder X ray diffraction pattern of the obtained nano quinacridonecrystal is shown in FIG. 3.

In FIG. 3, since 2 θ takes three peaks at 6.099, 13.816 and 26.153, thiscrystal is considered as γ type. Absorption spectrum of water dispersionliquid of nano quinacridone crystal prepared by changing theconcentration of the solution poured into water from 1 mM (a), 3 mM (b),5 mM (c) to 10 mM (d) are shown in FIG. 5.

FIG. 6( a) shows the absorption spectrum of dispersion of quinacridonecrystal prepared using water as a poor solvent, and two absorption peaksat 520 nm and 550 nm, and can be confirmed that the crystal is γ type.Further, the absorbance of the dispersion liquid increases in proportionto the concentration of the solution.

Example 2

Quinacridone pigment solution is prepared by same method as Example 1.200 μL of uniform solution whose concentration of organic pigment is 5mM is prepared. The prepared solution is poured into 10 mL of methanolvigorously stirred by a stirrer at 1500 rpm stirring speed. The size ofthe obtained fine particle of quinacridone pigment is measured by samemethod as Example 1, and average particle size and distribution curve ofthe obtained fine particle of quinacridone pigment are calculated.

Powder X ray diffraction pattern of the obtained nano quinacridonecrystal is shown in FIG. 4. Since the pattern has peaks at 26.870 of 2θ, said nano crystal of quinacridone can be confirmed as α type. Bychanging the kind of poor solvent, the kind of crystal form of theobtained quinacridone nano crystal can be controlled.

FIG. 6( b) shows the absorption spectrum of dispersion of quinacridonecrystal prepared using methanol as a poor solvent and absorption peakposition is beyond 600 nm, therefore can be confirmed as α type.According to the kind of poor solvent, it can be clearly confirmed thatthe fine particles of quinacridone pigment of different crystal form canbe obtained.

Example 3

5 mL of titanyl phthalocyanine pigment solution with 1 mM is preparedaccording to the method of the mentioned Examples, by exchanging thepigment for titanyl phthalocyanine and using 1:1 mixed solution ofNMP-pyridine as a solvent. Said solution is poured into 20 ml of mixedpoor solution of water and t-butanol, which is stirred vigorously at thespeed of 1500 rpm for one hour at room temperature. SEM image of theobtained nano crystal of titanyl phthalocyanine pigment is prepared bythe same as above mentioned Examples. Similarly to Example 1, SEM imageof the obtained fine particles is visually observed and the size offormed particles of the obtained nano crystal of titanyl phthalocyaninepigment is measured and distribution of average particle size isevaluated. SEM is shown in FIG. 1, distribution of particle size isshown in FIG. 7 and average size of crystal is 30 nm.

Powder X ray diffraction pattern of the obtained phthalocyanine nanocrystal is shown in FIG. 9. From only one strong peak at 26.49 of 2 θ,said crystal is confirmed as a new crystal form which was not founduntil now.

Further, the absorption spectrum of mixed poor solvent dispersion ofwater-t-butanol of titanyl phthalocyanine nano crystal is shown in FIG.10. Absorption peak is located at 900 nm, cut off wave length is 960 nmand has absorption band even in the range of longer wavelength region.This absorption characteristic is not found in a conventionalphthalocyanine crystal. Concerning these characteristics and the novelcharacteristics found by powder X ray diffraction, this crystal can beproved as a new crystal. Width of absorption of the crystal obtained inthis Example becomes broader than that of Y type, which has the highestperformance, having absorption width in the conventional titanylphthalocyanine crystal. Further, the crystal is very fine size and isuseful to be used as a dispersion thin film.

Example 4

2,9-dimethylquinacridone pigment possessing two substituted groups isdissolved in 200 μL of 1,3-dimethyl-2-imidazolidinone at roomtemperature so as the concentration to be 5 mM and a uniform solution isprepared. The prepared solution is poured into 10 mL of water withvigorously stirring at 1500 rpm using a stirrer.

Size and crystal form of the obtained fine quinacridone pigmentparticles are measured, and same results as Example 1, that is, 20 nmand γ type are obtained. And the tendency that the absorbance of thedispersion increases in proportion to the concentration of the solutionis also same as to Example 1.

INDUSTRIAL APPLICABILITY

As mentioned above, the present invention provides an excellent effectthat the high efficient method for preparation of fine particles oforganic pigment, especially, fine particles of nanometer size can beprovided, by using amide solvent as a solvent for preparation ofsolution and by combining with a poor solvent which can apply thetechnique to produce organic fine crystal by a reprecipitation method.Further, it is understood that, according to the selection of a poorsolvent, a pigment of different crystal form can be obtained, that is,the remarkable effect that a pigment of desired crystal structure can beobtained by simple change of production condition is provided by thepresent invention.

1. A method for preparation of concentrated fine nanoparticles oforganic pigment comprising, after dissolving organic pigment into anorganic solvent consisting of an amide solvent, pouring an obtainedpigment solution into a second solution, said second solution beingcompatible with said organic solvent and being a poor solvent to thepigment, by vigorously stirring.
 2. The method for preparation ofconcentrated fine nanoparticles of organic pigment of claim 1, whereinthe organic pigment is azo pigment, phthalocyanine pigment, quinacridonepigment, isoindolinone pigment, cyanine pigment, merocyanine pigment,fullerene pigment, polycyclic aromatic compound or polydiacetylenepigment.
 3. The method for preparation of concentrated finenanoparticles of organic pigment of claim 2, wherein the organic pigmentis phthalocyanine pigment or quinacridone pigment.
 4. The method forpreparation of concentrated fine nanoparticles of organic pigment ofclaim 3, wherein the amide solvent is selected from the group consistingof 1-methyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone,2-pyrrolidinone, ε-caprolactam, formamide, N-methylformamide,N,N-dimethylformamide, acetoamide, N-methylacetoamide,N,N-dimethylacetoamide, N-methylpropaneamide andhexamethylphospholictriamide.
 5. The method for preparation ofconcentrated fine nanoparticles of organic pigment of claim 1, whereinthe amide solvent is selected from the group consisting of1-methyl-2-pyrrolidinon, 1,3-dimethyl-2-imidazolidinone,2-pyrrolidinone, ε-caprolactam, formamide, N-methylformamide,N,N-dimethylformamide, acetoamide, N-methylacetoamide,N,N-dimethylacetoamide, N-methylpropaneamide andhexamethylphospholictriamide.
 6. The method for preparation ofconcentrated fine nanoparticles of organic pigment of claim 2, whereinthe amide solvent is selected from the group consisting of1-methyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone,2-pyrrolidinone, ε-caprolactam, formamide, N-methylformamide,N,N-dimethylformamide, acetoamide, N-methylacetoamide,N,N-dimethylacetoamide, N-methylpropaneamide andhexamethylphospholictriamide.
 7. The method for preparation ofconcentrated fine nanoparticles of organic pigment of claim 1, whereinpoor solvent is water, alcohol solvents, ketone solvents, ethersolvents, aromatic solvents, carbon disulfide, aliphatic solvents,nitrile solvents, sulfoxide solvents, halide solvents, ester solvents,ionic solution or a mixture of two or more thereof.
 8. The method forpreparation of concentrated fine nanoparticles of organic pigment ofclaim 2, wherein poor solvent is water, alcohol solvents, ketonesolvents, ether solvents, aromatic solvents, carbon disulfide, aliphaticsolvents, nitrile solvents, sulfoxide solvents, halide solvents, estersolvents, ionic solution or a mixture of two or more thereof.
 9. Themethod for preparation of concentrated fine nanoparticles of organicpigment of claim 3, wherein poor solvent is water, alcohol solvents,ketone solvents, ether solvents, aromatic solvents, carbon disulfide,aliphatic solvents, nitrile solvents, sulfoxide solvents, halidesolvents, ester solvents, ionic solution or a mixture of two or morethereof.
 10. The method for preparation of concentrated finenanoparticles of organic pigment of claim 4, wherein poor solvent iswater, alcohol solvents, ketone solvents, ether solvents, aromaticsolvents, carbon disulfide, aliphatic solvents, nitrile solvents,sulfoxide solvents, halide solvents, ester solvents, ionic solution or amixture of two or more thereof.
 11. The method for preparation ofconcentrated fine nanoparticles of organic pigment of claim 2, whereinsaid organic solvent is selected from the group consisting of1-methyl-2-pyrrolidinone, 2-pyrrolidinone,1,3-dimethyl-2-imidazolidinone and a mixed amide organic solventcontaining 1-methyl-2-pyrrolidinone, 2-pyrrolidinone or1,3-dimethyl-2-imidazolidinone in an amount that is more than 50 volume% of the organic solvent, and said poor solvent is water and/oralcoholic solvent.
 12. The method for preparation of concentrated finenanoparticles of claim 3, wherein said organic solvent is selected fromthe group consisting of 1-methyl-2-pyrrolidinone, 2-pyrrolidinoe,1,3-dimethyl-2-imidazolidinone and a mixed amide organic solventcontaining 1-methyl-2-pyrrolidinone, 2-pyrrolidinone or1,3-dimethyl-2-imidazolidinone in an amount that is more than 50 volume% of the organic solvent, and said poor solvent is water and/oralcoholic solvent.
 13. The method for preparation of concentrated finenanoparticles of claim 1 comprising, carrying out preparation of saidorganic solvent by dissolving an organic pigment by a condition fromheating at around maximum boiling point under atmospheric pressure toheating under supercritical state, then pouring an obtained concentratedorganic solvent of 0.5 mmol/L to 100 mmol/L into a poor solvent of alowest temperature of a liquid state.
 14. The method for preparation ofconcentrated fine nanoparticles of claim 2 comprising, carrying outpreparation of said organic solvent by dissolving an organic pigment bya condition from heating at around maximum boiling point underatmospheric pressure to heating under supercritical state, then pouringan obtained concentrated organic solvent of 0.5 mmol/L to 100 mmol/Linto a poor solvent of a lowest temperature of a liquid state.
 15. Themethod for preparation of concentrated fine nanoparticles of claim 3comprising, carrying out preparation of said organic solvent bydissolving an organic pigment by a condition from heating at aroundmaximum boiling point under atmospheric pressure to heating undersupercritical state, then pouring an obtained concentrated organicsolvent of 0.5 mmol/L to 100 mmol/L into a poor solvent of a lowesttemperature of a liquid state.
 16. The method for preparation ofconcentrated fine nanoparticles of claim 4 comprising, carrying outpreparation of said organic solvent by dissolving an organic pigment bya condition from heating at around maximum boiling point underatmospheric pressure to heating under supercritical state, then pouringan obtained concentrated organic solvent of 0.5 mmol/L to 100 mmol/Linto a poor solvent of a lowest temperature of a liquid state.
 17. Themethod for preparation of concentrated fine nanoparticles of claim 5comprising, carrying out preparation of said organic solvent bydissolving an organic pigment by a condition from heating at aroundmaximum boiling point under atmospheric pressure to heating undersupercritical state, then pouring an obtained concentrated organicsolvent of 0.5 mmol/L to 100 mmol/L into a poor solvent of a lowesttemperature of a liquid state.